Math behind Everquest...

[stifling]

The math behind bard songs is fairly simple. Only some effects change with level, mostly regen (hp/mana), stat bonuses, damage shields and damage over time... There is a range listed in the description of the song in the picture you have in the OP. the level 2 AoE song does between 2 and 18 damage based on level. so take your level and divide it by 60(65?) and multiply the ratio by the range of the song plus the initial value so for example.
You are level 45, and you play the level 2 song with no instrument:
45/60=.75
now multiply .75 by the range of the damage output
(18-2=16)
and you get .75*16 = 12,

Now add that to the base damage of 2 and at level 45 the song will do 14 damage to everything nearby.
Now instrument mods basically just take this final value and boost it by a set multiplier which is listed on the wiki (i added them for all instruments a while back) so looking at this particular song, it takes a stringed instrument modifier so if you played it while holding any instrument it would do more damage, the better the mod the higher the damage.
So if you use the store bought lute that you can find anywhere, it has a mod of 18 which will do 180% more damage, healing, etc. if you hold it while playing.
so that 14 dmg will now be 14*1.8=25.2 or 25 dmg (everquest always rounds down, even if the calculation is 25.999998, it will still be 25, annoying but predictable)

Now should you use the best stringed instrument currently available, the one from Silverwing in veeshans peak...
14*2.5 = 35dmg to everything around.